According to this article in in JKC, all Raymond C. Yard pieces made between 1920-1950 have been documented. The natural pearl necklace in question should be identifiable either through the still existing company or a jewellery historian.
Clasps on Raymond C. Yard's natural pearl strands were usually made of platinum. Not something that wears out or breaks. So one has to wonder what really happened to the clasp.
"Kuzmanovic?s research allowed her access to original special order and stock jewelry books from Yard, detailing every piece ever made; 36,000 special orders, 10,000 stock pieces, including details of the metals used, the stones, the client names, and stock numbers."
http://www.jckonline.com/blog/1950000195/post/1320017132.html
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